Guinea grass used to be known as Panicum maximum Jacq. In 2003, the subgeneric name Megathyrsus was raised to generic rank and the plant was renamed Megathyrsus maximus (Jacq.) B. K. Simon & S. W. L. Jacobs (Simon et al., 2003). However, the name Panicum maximum is still found in literature posterior to 2003.

Guinea grass (Megathyrsus maximus (Jacq.) B. K. Simon & S. W. L. Jacobs) is a major pantropical grass used throughout the tropics for pasture, cut-and-carry, silage and hay. It is a fast growing and leafy grass, which is palatable to livestock with a good nutritional value. However, it is generally recommended to supplement it with sources of protein in order to meet nutritional requirements or improve animal performance.

Morphology

Guinea grass is a large tufted, fast-growing perennial grass. It has a broad morphological and agronomic variability, ranging in height from 0.5 to 3.5 m, with stems of 5 mm to 10 mm diameter. There are two main types: a tall/medium tussock type, taller than 1.5 m at flowering, and a short tussock type (Cook et al., 2005). The root is a short creeping rhizome; culms are erect, hirsute at the nodes. Leaves are blade-shaped, glabrous to pubescent up to 35 mm broad. Inflorescence is a panicle, 15 to 50 cm long. Spikelets are 3-4 mm green to purple (Ecoport, 2009).

Utilization

Guinea grass is suitable for pasture, cut-and-carry, silage and hay. Many Guinea grass cultivars have been developed for different purposes and agronomic situations (FAO, 2009).

Distribution

Guinea grass is native to tropical Africa and is now widely naturalized in the tropics. It is naturally found in open grasslands, woodland and shady places within 16.3°N and 28.7°S.

It grows best under an annual rainfall above 1000 mm with no more than a 4 to 5 month dry period. Average annual day-temperature should range from 19.1°C to 22.9°C. Small types are more tolerant of cooler temperatures than tall types. It prefers well-drained, moist and fertile soils (Cook et al., 2005). It is tolerant of light frost and low soil pH if drainage is good (FAO, 2009) and also of high Al3+ saturation (Ecoport, 2009). It is well adapted to sloping, cleared land in rainforest areas (FAO, 2009). Drought tolerance depends on the cultivar, but should not generally exceed 4 or 5 months. Guinea grass can be sown with companion legumes such as Centrosema pubescens, Leucaena leucocephala, Pueraria phaseoloides or Macroptilium atropurpureum (Cook et al., 2005).

Forage management

Use for pasture, silage and hay

Guinea grass is well suited for cut-and-carry systems and can be used for making silage and hay. Guinea grass can be managed as a long-term pasture grass if grazed consistently, but it should not be grazed under 35 cm height, nor under very wet conditions (FAO, 2009). As the grass rest-period affects animal performance, a good rest-period is to wait for regrowth of 2.5 leaves/tiller (Candido et al., 2005). For silage and hay, a good cutting height is 60-90 cm, but for higher yields of acceptable quality it can be cut at up to 1.5 m, as it does not become coarse even if left to grow to that height (Hongthong Phimmasan, 2005). Better quality silage is obtained if Guinea grass is cut during pre-anthesis or anthesis (Sarwatt et al., 1989). Ensiled Guinea grass has a good texture and it was possible to mix grass of different ages with no effect on silage quality (Babayemi et al., 2009).

Guinea grass is a fast growing, bulky grass that helps prevention of soil erosion since it provides rapid ground cover (Roose, 1994). While it spreads slowly when it is well managed, Guinea grass can spread very fast and become a weed in ungrazed areas where soil disturbance has occurred. It is a major weed in sugarcane fields since it grows well in shaded conditions (Ecoport, 2009).

Nutritional aspects

Potential constraints

Traces of HCN in Guinea grass are reported as well as small amounts of oxalic acid (0.28%) (Ndyanabo, 1974 cited by FAO, 2009). Continuous feeding of oxalates has been implicated in hyperparathyroidism ("big head") in horses, and occasionally nephrosis or hypocalcaemia in ruminants (Miyazaki et al., 2003).

In South Africa, it is suspected to cause photodermatitis in sheep ("dikoor", literally "thick ear"), perhaps in conjunction with the smut fungus Ustilago (Botha et al., 2002). The plant is also said to cause fatal colic if eaten too wet or in excess, particularly in Equidae (Duke, 1983; Cerqueira et al., 2009).

Ruminants

Guinea grass is a valuable fodder for pasture, hay and silage. However, it is generally preferable to supplement it with sources of protein to improve animal performance.

Palatability

Guinea grass is well eaten by all classes of grazing livestock, with particularly high intakes of young leafy plants (Cook et al., 2005).

Digestibility

Reported OM digestibility values range from 53 to 79%. The best OM and DM digestibilities are obtained with young regrowth (Peiris et al., 1995).